Short Messaging Service (SMS) is a technology for sending and receiving short text messages between mobile users. It was first introduced in the Global System for Mobile Communications (GSM) standards in the 1990s but was subsequently included in other wireless standards such as Code Division Multiple Access Systems (CDMA). Although SMS is extremely popular, one of its biggest drawbacks is that an SMS message can only carry a small amount of data due to limitations imposed by the Mobile Application Part (MAP) protocol of SS7. An SMS message can only contain up to 160 8-bit alphanumeric or binary characters and any message longer than 160 characters is usually sent in multiple messages.
A Short Messaging Service Centre (SMSC) is responsible for handling the delivery of SMS messages in a wireless communications network. An SMS message sent by a mobile user is first delivered to the user's network SMSC before being routed to the recipient. If the recipient's network is operated by a different provider or employs a different wireless standards, the message may pass more through more than one SMSC or SMSC gateway before reaching its final destination. Signalling System 7 (SS7) provides the transport mechanism for SMS traffic.
There are several messaging services that provide an extension to SMS. Enhanced Messaging Service (EMS), which uses existing SMS infrastructure, allows up to 255 SMS messages to be packaged as one EMS message having richer content such as animation, pictures, sounds and formatted text. Unlike SMS and EMS, Multimedia Messaging Service (MMS) messages are delivered using a mobile packet data network. MMS was first introduced in 2.5 generation networks such as GPRS, which provides an Internet Protocol (IP) overlay to the existing GSM networks. A multimedia message may contain images, audio clips and videos.
On the other hand, Mobile Instant Messaging (MIM) technology enables mobile devices to engage in real-time, instant messaging via an IP data network. Users need to register a user name tag or “handle” with an instant messaging service provider to send and receive messages. Many current MIM services also require users to maintain a persistent connection with the Internet during a chat session.